Personal computers have become commonplace in the modern workplace. Many personal computers contain a rigid memory disk or hard drive. A hard drive involves a rigid metal or non-metal disk as the substrate of the magnetic medium. In one conventional arrangement, the thin film rigid disks are manufactured by electroless nickel plating a thin-film of nickel or nickel alloy (e.g., nickel/phosphorous, Ni-P) onto an aluminum base. The Ni-P coating is then polished to a very fine, mirror-like finish. After polishing, the Ni-P coating is textured, followed by the application of a magnetic coating(s) thereon to form the magnetic medium. However, nonmetal substrates, such as glass or ceramic substrates, also are used in the rigid memory disk industry in place of the metal substrates. For these nonmetallic substrates, there is no metal or metal alloy coating applied onto the substrate before subsequent polishing, texturing and magnetic coating application. Rather, the surface of the glass or ceramic rigid disk itself is polished, textured, and thereafter the magnetic coating is directly applied thereon without interposing any metal or metal alloy coating layer.
The texturing portion of this process is critical to the performance of the rigid disks. Texturing accomplishes a number of purposes. For example, texturing improves the magnetic properties of the coated disks. The scratches formed during texturing are critical to reducing the magnetic domain size thereby increasing the disk storage capacity. A textured surface also reduces the static friction between the head (which reads and writes data on the disk) and the disk. When the computer is turned on and energized, the rigid disk will begin to spin. If the disk is smooth and untextured, this head/disk contact makes it difficult for the disk to start spinning. This is known in the computer industry as stiction/friction. Finally, texturing may improve the aerodynamics between the head and the thin film rigid disk as the disk spins beneath the head.
The texturing process is traditionally accomplished by using a loose abrasive slurry. The loose abrasive slurries provide substantially circumferential scratches that have sharply defined edges having the requisite depth. Loose abrasive slurries are, however, accompanied by a number of disadvantages. For instance, the loose abrasive slurries create a large amount of debris and waste. As a result, the thin film rigid disks must be thoroughly cleaned to remove any residues left on their surface from the binder precursor. Also, abrasive particles from the abrasive slurry may become embedded in the surface of the rigid disks which may cause damage to the sensitive MR heads used in modern disk drives. Finally, the loose abrasive slurry also results in a relatively high amount of wear on the equipment used for texturing.
To overcome the disadvantages associated with loose abrasive slurries, coated abrasive lapping tapes have been used to texture the thin film rigid disks. An example of such a product is xe2x80x9cIMPERIALxe2x80x9d Lapping film (Type R3) commercially available from 3M Company, St. Paul, Minn. This lapping film comprises a polymeric film backing having an abrasive coating layer bonded thereto. The abrasive coating layer consists of very fine abrasive particles (average particle size less than 10 micrometers) dispersed in a binder and coated on the polymeric film to form a thin layer (about 10-15 micrometers). The surface profile of the abrasive coating is essentially flat other than the partial protrusions formed by some of the fine abrasive particles. During use, the lapping film abrades a portion of the substrate surface, thereby texturing the surface of the substrate. Similarly, U.S. Pat. No. 4,974,373 to Kawashima et al. describes an abrasive tool suited for use in lapping, polishing, texturing, and various other finishing of precision machine parts, mentioning hard disks, magnetic heads, ceramics, plastics, and jewels. The tool is formed from abrasive powder particles fixed in a separated proximity to each other in a binder resin coat as a continuous monolayer disposed on a plastic film base. Japanese laid-open application no. 5-228845 of Tokyo Magnetic Printing Co. Ltd, published on Sep. 7, 1993, discloses a texturing polishing film for magnetic disk substrates, where the polishing film involves abrasive particles retained on a plastic film or nonwoven fabric tape with a water soluble resin, preferably as a single particle layer.
The portion of the substrate abraded away during texturing is known in the industry as swarf. Practice has shown that swarf generated during the use of such lapping films having sealed backings and nonstructured abrasive coatings is still apt to be present at the interface of the abrasive coating and the substrate work surfaces. Therefore, there remains some opportunity for the swarf to become attached to the high spots on the textured rigid substrate where lapping films are employed. That particular phenomenon is known in the industry as reweld. Those high spots are highly undesirable as they can collide with the computer head during use, which can cause a loss of data and/or head damage as a result of the collision.
In addition to the problems with reweld, the lapping film may not provide scratches having edges as sharp and/or clean as those produced by the loose abrasive slurries. These lower quality scratch edges may degrade the quality of the disks manufactured using lapping film for the texturing process.
The use of structured abrasive articles has been described recently where abrasive composites are formed on flexible backings in the form of rows of aligned individual abrasive composites or as elongate ridges of abrasive material. For instance, U.S. Pat. No. 5,152,917 (Pieper et al.) discloses structured abrasive articles with abrasive composites that are precise three-dimensional shapes extending from the backing. Recesses or channels are left between the abrasive composite shapes to facilitate the discharge of swarf from the abrasive article and thereby reduce loading. Pieper et al. do not disclose the use of their abrasive article for texturing and/or buffing rigid disks.
Also, U.S. Pat. No. 5,107,626 (Mucci) describes a method for treating a workpiece by a structured abrasive article to produce a precise pattern on the workpiece surface, where the workpiece is described as any solid material. The examples of solid materials given by Mucci include metal and metal alloys, such as carbon steel, stainless steel, high nickel alloys and titanium, as well as other disparate surfaces such as plastic, painted surfaces, ceramics, wood, marble, stone and the like. Mucci, like Pieper et al., does not report the use of the abrasive article for texturing and/or buffing rigid disks.
U.S. Pat. No. 5,733,178 (Ohishi) reports a method for texturing magnetic recording media substrates using a structured abrasive article including a flexible backing having a major surface and an abrasive coating including a plurality of precisely-shaped three-dimensional abrasive composites. The abrasive composites comprise a plurality of abrasive particles dispersed in a binder which binder provides the means for attachment of the composites to the backing.
The present invention provides a method of mechanically treating a substrate, the method comprising the steps of:
(a) providing a substrate for mechanical treatment, the substrate selected from the group consisting of a rigid disk or a rigid disk substrate;
(b) providing an abrasive article in contact with the substrate at a pressure, the abrasive article comprising:
a backing having a first major surface and a second major surface; and
an abrasive coating consisting essentially of:
a hardened binder coating having a first surface adhered to the flexible backing and a second structured surface comprising a plurality of precisely-shaped protrusions; and
a diamond-like carbon coating superposed and adhered to at least a portion of the structured surface of the hardened binder coating; and
(c) moving at least one of the substrate and the abrasive article relative to the other to provide the mechanical treatment.
The present invention provides a method of mechanical treatment of a substrate wherein mechanical treatment is used broadly to include the processes of texturing, buffing, or cleaning. xe2x80x9cTexturingxe2x80x9d as used herein refers to the process of generating scratches in a rigid disk substrate prior to the application of the magnetic coating(s) to the rigid disk substrate. xe2x80x9cBuffingxe2x80x9d as used herein refers to the process of removing asperities in the surface of the rigid disk or rigid disk substrate. xe2x80x9cCleaningxe2x80x9d as used herein refers to the process of removing contamination, for example, particulate contamination, from the surface of the rigid disk or rigid disk substrate without altering the surface topography of the rigid disk or rigid disk substrate.
In an embodiment of the method of the present invention, the substrate is a rigid disk substrate comprising a metal base having opposite major surfaces and a metal coating formed on at least one of the major surfaces. In another embodiment, the substrate is a rigid disk substrate comprising glass or ceramic. In another embodiment of the method of the present invention, the substrate is a rigid disk.
In another embodiment, the substrate is circular having a center and wherein step (c) comprises rotating the substrate about the center to form substantially circumferential scratches in the substrate.
In another embodiment of the method of the present invention the mechanical treatment is performed in a liquid environment by introducing a liquid between the abrasive article and the rigid disk or rigid disk substrate.
In another embodiment of the method of the present invention the abrasive article is oscillated in a direction substantially perpendicular to the direction of travel of the substrate.
The present invention also provides an abrasive article comprising:
a backing having a first major surface and a second major surface; and
an abrasive coating consisting essentially of:
a hardened binder coating having a first surface adhered to the flexible backing and a second structured surface comprising a plurality of precisely-shaped protrusions; and
a diamond-like carbon coating superposed and adhered to at least a portion of the structured surface of the hardened binder coating.
In one embodiment of the abrasive article of the present invention, the diamond-like carbon coating has a thickness ranging from about 5 nm to 1 micrometer. In another embodiment, the diamond-like carbon coating has a plasmon energy greater than about 26 eV.
In another embodiment, the plurality of precisely-shaped protrusions have shapes selected from the group consisting of cubes, prisms, cones, truncated cones, pyramids, and truncated pyramids.
In another embodiment, the parallel elongate ridges each comprise a continuous protrusion of hardened binder extending continuously between the side edges of the backing. In another embodiment, the continuous protrusion is a pyramidal shape having an apex and sides, the sides intersecting at said apex to form an angle therebetween of from about 70 to about 110 degrees. In another embodiment, the ridges each comprise a plurality of separate precisely-shaped protrusions aligned with transverse centers located on said machine direction axis.
In another embodiment, the backing is polyethylene terephthalate film having a thickness between about 25 and 125 micrometers.
In another embodiment, the binder is an acrylate or a methacrylate.